Use any E-Commerce plugin.
Which you use is up to you, pretty much all of them do the job. Create a product for your image, set the low res image as the featured image, or some content imag, then set it up as a digital/download product with the file being the original high resolution image.
How you would do this would depend on the plugin used. Which you use I will not go into as that is a job for another question ( and such a question would be a plugin recommendation question which would be offtopic, and closed by moderation )